How do they get the variable cost per unit?

The Wild Boar Corporation is working at full production capacity producing 10,500 units of a unique product, Everlast. Manufacturing cost per unit for Everlast is as follows: (Click the icon to view the cost per unit information.) A customer, the Apex Company, has asked Wild Boar to produce 2,500 units of Stronglast, a modification of Everlast. Stronglast would require the same manufacturing processes as Everlast. Apex has offered to pay Wild Boar $54 for a unit of Stronglast plus half of the marketing cost per unit. Read the Requirement 1. What is the opportunity cost to Wild Boar of producing the 2,500 units of Stronglast? (Assume that no overtime is worked.) Determine the formula for calculating the opportunity cost, then calculate the opportunity cost of producing the 2,500 units of Stronglast. Data table Manufacturing overhead cost per unit is based on variable cost per unit of $7 and fixed costs of $84,000 (at full capacity of 10,500 units). Marketing cost per unit, all variable, is $4, and the selling price is $58